Apparatus and method for retaining a catheter in a blood vessel in a fixed position

ABSTRACT

A method and apparatus for retaining a catheter tip in a fixed position within a blood flow and preventing it from contacting a blood vessel wall. The apparatus includes a tip retainer at the distal end of the catheter that anchors the tip of the catheter within the blood vessel. The catheter tip is retained within the blood vessel spaced from the wall to ensure that it does not contact the wall of the blood vessel. This reduces damage to the blood vessel caused by chronic movement and contact between the catheter tip and the wall of the blood vessel. In one embodiment, the tip retainer includes a prong that penetrates the wall of the blood vessel, thus preventing the catheter tip from moving longitudinally within the blood vessel. In alternative embodiments, the tip retainer contacts the wall but does not penetrate the wall.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.08/137,619, filed Oct. 15, 1993 now U.S. Pat. No. 5,509,900 which is acontinuation in part of U.S. patent application Ser. No. 07/844,715,filed Mar. 2, 1992 now abandoned.

TECHNICAL FIELD

This invention relates to intravascular catheters that have means forreducing stenosis and thrombosis at the tip of the catheter.

BACKGROUND OF THE INVENTION

The treatment of a number of medical conditions requires the placementof catheters within a patient's blood vessel for an extended period oftime. These longterm applications include blood access for hemodialysis,chemotherapy, parental nutrition, blood transfusions and blood sampling.

Vascular access with catheters was first introduced more than 20 yearsago. With the advent of soft, flexible silicone double lumen catheters,both acute and chronic hemodialysis became a routine procedure. Althoughsubclavian dialysis catheters are easily inserted and well tolerated,catheter lifespan averages about three months. This is of great concernto patients on maintenance dialysis.

It is well known in the medical field that chronic placement of acatheter in a patient's blood vessel often results in catheter failuredue to aspiration of the blood vessel wall into the tip of the catheter,clot or thrombus formation at the tip of the catheter, or stenosisaround the tip of the catheter. A catheter failure resulting from one ormore of these mechanisms is evidenced by an inability to aspirate and/orinfuse fluid through the catheter, generally referred to as catheterocclusion. Typically, catheter occlusions caused by aspiration of theblood vessel wall or clot formation at the catheter tip may be resolvedby repositioning the catheter tip or infusing antithrombotic agents.

Stenosis is a narrowing of the blood vessel lumen as seen in a venogramand, in general, can be due to either the formation of a thrombus withinthe blood vessel or a thickening of the blood vessel wall. The generallyaccepted view is that stenosis around the tip of a catheter implantedwithin a blood vessel is due to the formation of a thrombus resultingfrom a biochemical reaction to the introduction of a foreign materialinto the blood vessel. Previous attempts to prevent catheter occlusionhave centered around thromboresistant coatings on the catheter surfacein order to prevent the biochemical reaction of the patient's blood tothe material of which the catheter is formed.

Prior art related to the present invention deals with the placement ofstents within a diseased blood vessel to treat the problems associatedwith stenosis. Stents range from simple wire meshes used in U.S. Pat.No. 4,800,882, to a canister made of hydrophilic plastic which expandsupon placement in a blood vessel as in U.S. Pat. No. 4,434,797. Stentsare typically secured to a deployment catheter for insertion into thepatient's blood vessel via a percutaneous procedure. Surgical placementof these stents is achieved by feeding the catheter from a distant site,e.g., a percutaneous puncture into the femoral artery, to the stenosistarget. The deployment catheter is then removed, leaving the stentwithin the blood vessel lumen.

Prior publications on the subject of mounting devices in the bloodstream include "Registration of Phoric Changes of Blood Flow by Means ofa Catheter-Type Flowmeter," by Heinz Pieper printed in The Review ofScientific Instrument 29(11):965-967, November 1958, and U.S. Pat. Nos.4,425,908; 4,936,823; 4,813,930; 5,135,517; and 4,654,028. However, noneof these address and solve the problems presented in the field of thepresent invention.

SUMMARY OF THE INVENTION

The present invention is directed to an intravascular catheter that hasmeans to retain the tip of the catheter within a blood vessel lumen suchthat the tip of the catheter is prevented from contacting the wall ofthe blood vessel. This prevents repeated impact between the catheter tipand blood vessel wall. This reduces denudation and damage to theendothelial and smooth muscle cells that line the blood vessel wall. Byreducing damage to these cells, the invention allows for the cells tocontinue to release the bioactive molecules that normally prevent andreverse the thrombotic and coagulation processes in blood.

Most vascular injury research is in the area of arterial injury;however, the mechanism that regulates cellular growth in injured veinsis not known. It is a reasonable assumption that the "response to injuryhypotheses" proposed in Ross, R., Glomset, J. A., "The Pathogenesis ofAtherosclerosis," N. Engl. J. Med. 2:369-77, 1976, can also be appliedto injuries in the venous system. This hypothesis is based on thefollowing observations after injury to the lumen of the blood vessel:(1) platelet adherence and degranulation precedes smooth muscle cellproliferation; (2) intimal thickening in injured arteries ofthrombocytopenic animals is reduced; (3) platelet granules containpotent mitogens for cultured smooth muscle cells. Based upon theseobservations, Ross and Glomset suggested that a high local concentrationof growth factors, particularly platelet-derived growth factors releasedfrom degranulating platelets could stimulate smooth muscle cellproliferation. Their hypothesis is based on a relationship between thethrombosis that occurs within an injured vessel and the subsequent cellgrowth associated with repair of the injured vessel wall.

Normally, hemostasis results from a delicate balance betweenclot-stimulating and clot-inhibiting processes. Endothelial cells andsmooth muscle cells in a normal blood vessel are probably the mainsource of clot regulating factors such as heparin or heparan sulfate.These heparin and heparin-like molecules prevent the adherence of bloodproteins and platelets to the surface of a normal blood vessel. Sincethe endothelium is a critical component of hemostasis control, localizedinjury and denudation of the endothelium by repeated impact with acatheter tip results in a shift of this delicate balance toward clot andthrombus formation within a denuded region. This clot formation mayoccur even if the catheter is composed of a material that normally wouldnot create a reaction in the body.

Physical damage to the wall of the blood vessel affects the release andproduction of a number of growth-stimulating factors such as basicfibroblast growth factor and platelet-derived growth factor. Thesegrowth factors help to overcome the antiproliferative activities of theheparan sulfates, thus helping to initiate cellular proliferation andthe migration of smooth muscle cells that ultimately leads to stenosis.Therefore, preventing physical damage to the endothelial cell lining ofthe blood vessel wall reduced stenosis, as well as thrombosis, at thetip of the catheter.

Prior art catheters allow chronic and repeated contact between thecatheter tip and the wall of the blood vessel, resulting in damage tothe blood vessel as discussed previously. The tip of the catheter mayrepeatedly bump into different locations inside the blood vessel, or thesame location a number of different times, causing a reaction, or worse,damage to the vessel wall. Further damage is caused by the aspiration ofthe blood vessel wall into the catheter lumen. This occurs when blood iswithdrawn through the catheter, such as in the performance of dialysis.

The present invention solves the problems by approaching them from anentirely different view than the prior art attempts; namely, bypreventing repeated impact between the catheter tip and the blood vesselwall. The inventor has found that repeated impact with the vessel walland a catheter tip, even if it is a soft tip, causes a physical reactionin the blood vessel wall. This reaction occurs because of repeatedcontact between the catheter tip and the wall of the blood vessel evenif the catheter tip is soft, and even if the tip is properly coated withantithrombotic agents. This catheter-induced reaction in the bloodvessel wall may lead to the formation of a mural thrombus and/orabnormal cellular proliferation within the blood vessel wall, thusresulting in stenosis and catheter occlusion. Prior art efforts toprevent catheter occlusion through the use of thromboresistant coatingsdo not alleviate the physical reaction that the catheter tip may causeto the blood vessel wall by repeated impact. Therefore, chronicplacement of a catheter in a patient still results in catheter occlusionin the majority of cases.

In accordance with aspects of the present invention, chronic contactbetween and aspiration of the blood vessel wall by the catheter tip isprevented. This reduces damage to the endothelial cells lining the bloodvessel, thus reducing catheter occlusion due to stenosis and thrombosis.In addition, the occurrence of catheter occlusion resulting fromaspiration of the vessel wall will be reduced.

The present invention includes, in one embodiment, an antistenoticintravascular catheter for insertion into a blood vessel. The catheterincludes a tip retainer, located at the distal end of the catheter, forretaining the tip of the catheter within the blood vessel and preventingthe catheter from contacting the wall of the blood vessel. The tipretainer positions the tip of the catheter within the blood vesselwithout substantially obstructing fluid flow through the blood vessel.The catheter also includes an internal passageway for permitting fluidsto pass through the catheter. Preferably, the catheter is a double lumencatheter of the type used generally in kidney dialysis.

In all embodiments, the tip of the catheter is retained in the bloodvessel by anchoring the tip with respect to the wall of the bloodvessel. Advantageously, the tip retainer permits some movement of thecatheter tip with respect to the vessel wall, such as slight movementforward and back or side to side with the pulsation of the blood flow.However, movement is restricted to minimize repeated contact (or allcontact) of the tip with the blood vessel wall. Just as the anchor of aship anchors a ship to the bottom but permits some movement of the shipas the water rises and falls or flows, similarly the tip retainer can besaid to anchor the tip to the vessel wall but still permit some movementof the tip based on changes of the flow in which it is anchored.

Numerous alternative embodiments are disclosed for the tip retainer. Insome embodiments, the tip retainer does not penetrate the wall of theblood vessel. In one embodiment, the tip retainer includes a penetratingmember that does penetrate the blood vessel wall. In all embodiments,the tip of the catheter is retained in the blood vessel by anchoring thetip with respect to the wall of the blood vessel.

In one preferred embodiment, the tip retainer is two or more loops ofwire that flex outward and contact the wall. The loops do not penetratethe wall tissue, but do anchor the tip in a fixed position in the bloodvessel, retaining it in the blood flow and preventing contact of the tipwith the vessel walls.

In another preferred embodiment, a single loop extends from the tipportion of a double lumen catheter. The single loop is composed of aflexible wire coated with silicone, silicone tubing or, alternatively,is composed of silicone tubing alone. The diameter of the loop isselected to be sufficiently large that the loop bridges any branches inthe blood vessel which are likely to be encountered when the catheter ispositioned within the blood vessel.

As a further alternative, the silicone tubing which forms the loop maybe in fluid communication with the lumen of the catheter separate fromthe lumen used for the kidney dialysis. Medication can be deliveredthrough the lumen for delivery to the walls of the blood vessel at thepoint of contact by the loop. This provides the distinct advantage thatanticoagulant medication can be delivered specifically to walls of theblood vessel near the catheter tip.

In a further embodiment the tip retainer includes fletching to anchorthe catheter tip in the blood vessel. Alternatively, the tip retainer isa plurality of single straight wires that are prestressed to flexoutward or straight wires with loops on the end.

In accordance with one embodiment of the invention, the tip retainerincludes penetration means for penetrating the wall of the blood vesseland preventing the tip of the catheter from moving longitudinally withinthe blood vessel. In this embodiment, the tip includes a loop forlimiting the depth of penetration.

In one embodiment of the invention, a plurality of members run from theproximal end of the catheter to the distal end where they extendradially outward until they contact the wall of the blood vessel. Inthis embodiment, the catheter includes withdrawal means for withdrawingthe positioning means into the catheter such that the positioning meansis prevented from damaging the wall of the blood vessel when thecatheter is withdrawn from the blood vessel. The withdrawal meansincludes a guideway that runs from the proximal end of the catheter tothe distal end of the catheter. The positioning means extends from theproximal end to the distal end of the catheter within the guideway.

According to one aspect of the present invention, a method for reducingcatheter failure due to stenosis or thrombosis at a catheter tip isprovided.

Positioning means is attached to the catheter tip, and the catheter tipand attached positioning means are placed within the blood vesselwithout substantially obstructing fluid flow through the blood vesseland such that the catheter tip is prevented from contacting the bloodvessel wall.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first preferred embodiment of theantistenotic intravascular catheter of this invention.

FIG. 2A is an enlarged perspective view of a first preferred embodimentof the tip retainer as deployed.

FIG. 2B is an enlarged perspective view of the preferred embodiment ofFIG. 2A showing the tip retainer after it has been partially withdrawninto the guide tube.

FIG. 3 is an enlarged perspective view of the distal end of a secondembodiment of the tip retainer.

FIG. 4 is an enlarged perspective view of an alternative embodiment forconnecting the tip retainer to the catheter.

FIG. 5 is an enlarged perspective view of an alternative embodiment ofthe tip retainer.

FIG. 6 is an enlarged perspective view of an alternative embodiment ofthe tip retainer.

FIG. 7 is an enlarged perspective view of a further alternativeembodiment of the tip retainer.

FIG. 8 is an enlarged perspective view of a further alternativeembodiment of the tip retainer.

FIG. 9 is an enlarged perspective view of a further alternativeembodiment of the tip retainer.

FIG. 10A is an enlarged perspective view of a further alternativeembodiment of the tip retainer.

FIG. 10B is an end view of the device of FIG. 10A.

FIG. 11 is a perspective view of a further alternative embodiment of thecatheter showing an alternative embodiment of the tip retainer.

FIG. 12 is an enlarged view of a further alternative embodiment of thetip retainer.

FIG. 13 is an enlarged view of a further alternative embodiment of thetip retainer.

FIG. 14 is an enlarged view of a further alternative embodiment of thetip retainer.

FIG. 15 is an enlarged view of a further alternative embodiment of thetip retainer.

FIG. 16 is an enlarged view of a further alternative embodiment of thetip retainer.

FIG. 17A is a top view of the embodiment of FIG. 15 using fletchingattached straight as the tip retainer.

FIG. 17B is a top view of an alternative embodiment of FIG. 17A.

FIG. 18 is an end view of the embodiment of FIG. 17A as installed withina large blood vessel.

FIG. 19 is an end view of the embodiment of FIG. 17A as installed in asmall blood vessel.

FIG. 20 is a top view of an alternative embodiment using fletchingattached at a cant as the tip retainer.

FIG. 21 is an end view of the embodiment of FIG. 20.

FIGS. 22-24 illustrate a further alternative embodiment for placing thecatheter having the tip retainer on the end thereof within a bloodvessel.

FIG. 25 is a side elevational view of a further alternative embodimentof the tip retainer.

FIG. 26 is an end view of the embodiment of FIG. 25.

FIG. 27 is a side elevational view of the catheter having the tipretainer of FIG. 25 in one of the possible positions inside a bloodvessel.

FIG. 28A is an enlarged view of a further alternative embodiment of theretainer and catheter.

FIG. 28B is an end view of the catheter used in the embodiment of FIG.28A, without the tip retainer shown.

FIG. 28C is an end view of a further alternative embodiment of thecatheter of FIG. 28A without the tip retainer shown.

FIG. 29 is an enlarged elevational view of a further alternativeembodiment of the tip retainer including a medication delivery system.

FIG. 30 is a side elevational view of a further alternative embodimentpositioned at a possible location within the blood vessel.

FIG. 31 is an enlarged elevational view of a further alternativeembodiment of the tip retainer.

FIG. 32 is an end view of the embodiment of FIG. 31.

FIG. 33A is a side elevational view of a further alternative embodimentof the tip retainer.

FIG. 33B is a further alternative embodiment of the tip retainer of FIG.33A.

FIG. 34 is an end view of the tip retainer of FIGS. 33A and 33B.

FIG. 35 is a top plan view of a further alternative embodiment of thetip retainer mounted on an alternative embodiment of the catheter.

FIG. 36 is a side elevational view of the embodiment of FIG. 35.

FIG. 37 is a side elevational view of a further alternative embodimentof the tip retainer.

FIG. 38A is a side elevational view of a further alternative embodimentthe tip retainer in an extended position for insertion.

FIG. 39B is a side elevational view of the embodiment of FIG. 38A withthe tip retainer in a bode position for positioning within a bloodvessel.

FIG. 39 is a side elevational view of a further alternative embodimentof the tip retainer.

FIG. 40 is a side elevational view of a further alternative embodimentof the tip retainer.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a perspective view of a first preferred embodiment of anantistenotic intravascular catheter 2 of the present invention. Catheter2 includes a tube 4 formed from a material suitable for placement in ablood vessel, such as silicone rubber. The catheter includes a Dacronanchor cuff 14 for anchoring the catheter subcutaneously. An in-lineclamp 16, for preventing fluid flow, is placed on tube 4 adjacent theproximal end 6. The proximal end 6 of the catheter is attached to aluer-lock adapter 18 which is sealed by threading an injection sealingcap 20 onto the adapter in a manner known in the art.

According to one aspect of one embodiment of the present invention, theintravascular catheter 2 includes a tip retainer 9 for retaining thedistal end 8 in the bloodstream and preventing the tip of the catheterfrom contacting the wall of a blood vessel 30 as shown in FIG. 2A.

In a first embodiment, the tip retainer 9 includes four wires 12positioned within the catheter wall and extending along the length ofthe catheter, from the distal end of the catheter towards the proximalend 6 of the catheter. This ensures that the proximal ends 34 of thewires 12 will be accessible outside the patient's body after thecatheter has been implanted in a blood vessel 30. The proximal ends 34of the wires 12 are secured to the catheter by an appropriate methodsuch as heat shrink Teflon™ tubing 32 that is placed over the wires andshrunk in place. The proximal end of the wires could also be securedthrough the use of a band integrally formed in the tube 4 or otherstructures which prevent movement of the proximal end 34 of the wires 12until they are controlled by a physician.

The wires 12 are preferably made of or coated with a material which doesnot cause an adverse reaction when placed in the patient's body.Suitable materials include stainless steel, titanium, some plastics suchas nylon, some composite materials, and Teflon™ coated wires, includingTeflon™ coated stainless steel. Depending upon the application, thewires 12 have a diameter ranging from 0.0025 to 0.076 cm. In someapplications, it may be desirable to treat the wires 12 with anantithrombotic coating, for example, dipping or plating the wires in acoating or applying a coating through plasma polymerization in order toreduce blood clotting on the wires. Plasma polymerization is explainedin detail in Yeh et al., "Blood compatibility of surfaces modified byplasma polymerization," Journal of Biomedical Materials Research22:795-818, 1988.

As shown in FIG. 2A, in one embodiment, the wires 12 extend along thelength of the catheter through guideways 38 and exit the guideways atopenings 40. The guideways 38 protect the wires 12 while alsomaintaining proper positioning between the individual wires. Guideways38 and wires 12 are preferably extruded as an integral part of tube 4,or alternatively are extruded individually and are later attached ontothe outside of the tube 4 or inserted into tube 4. In the embodimentshown, four wires 12 are used, however, a different number of wires,such as three or five, could be used, depending upon the application.

Preferably, the four wires 12 are equally spaced circumferentiallyaround the distal end 8 such that they serve as a tip retainer 9 andpositioning means for positioning the tip of the catheter within theblood vessel 30. The tip retainer ensures that the tip of the catheterdoes not contact the inner wall 27 of the blood vessel 30. The thinwires 12 restrict movement of the tip of the catheter to prevent it fromhitting the inner wall 27 while not substantially obstructing the fluidflow through the blood vessel and not causing clots.

In the embodiment illustrated in FIG. 2A, a loop 25 is formed near theend of each wire 12, and a short penetration prong 26 is formed thatextends outwardly from each loop. The prongs 26 penetrate the wall ofthe blood vessel 30. Each prong 26 is sized and extends from loop 25such that the prong penetrates the wall of the blood vessel to a depthin the range of 0.1 to 3 mm after placement within the blood vessel. Theloops 25 serve as limiting means for limiting the depth to which theprongs 26 penetrate. This prevents the tip 8 of the catheter from movinglongitudinally within the blood vessel 30.

Other structures could also be used to perform the penetration and depthlimiting functions. As an example, instead of forming a loop near theend of each wire, an enlarged section such as thickening of the wireband welded or bonded to the wire or a bend near the tip of the wirecould be used.

The distal end of the catheter is retained within the blood vessel andprevented from contacting the endothelial cells lining the blood vesselby rubbing or aspirating the wall of the blood vessel by the tipretainer 9. Additionally, noncontact damage to the endothelial cells ofthe blood vessel, such as through fluid dynamics wherein the force ofthe flow of fluid around the openings of the catheter may cause cellulardamage, is believed to be reduced by the present invention. Althoughpenetration of the wall 27 by prongs 26 causes some damage to the bloodvessel, the damage caused is not significant in comparison to the damagethat would be caused by repeated impact or chronic rubbing of the tip 8or by aspiration of the inner wall 27, which may occur with prior artcatheter designs. By reducing the contact with and damage to theendothelial cells, the present invention allows for the continuedrelease of anticoagulant molecules by the endothelial cells in thevicinity of the distal end of the catheter as explained previously.Correspondingly, there is a reduction in thrombosis and/or stenosis ofthe blood vessel lumen at the distal end of the catheter and thusreduced catheter occlusion.

The antistenotic intravascular catheter 2 (FIG. 1) may be placed withinthe blood vessel 30 using a sheath introducer of the type shown in moredetail in FIGS. 22-24, an embodiment of which is explained with respectto those Figures. In one embodiment, a tubular introducer sheath isinserted within a patient's blood vessel, with the sheath terminating atthe point within the blood vessel where the distal end 8 of the catheteris to be placed. The catheter 2 is then placed within the introducersheath with the wires temporarily constrained along the catheter'slongitudinal axis by the sheath. The catheter is then pushed down thesheath until the distal end 8 of the catheter exits the introducersheath. As the distal end of the catheter exits the introducer sheath,the wires 12 spread radially to contact and penetrate the blood vesselwall as shown in FIG. 2A. After placement of the catheter into the bloodvessel, the introducer sheath is removed from the blood vessel.

Another technique for placing the inventive catheter tip retainer withinthe blood vessel wall is with an inflatable balloon. Small balloons forinsertion into the blood stream and methods to inflate them are known inthe field of medical treatment devices. According to one aspect ofinstalling this invention, the wires 12 are positioned circumferentiallyaround such a deflated balloon. The balloon is then introduced into theblood vessel by any acceptable technique. When the tip of the catheteris at the proper location, the balloon is inflated and the wires 12contact the wall 30. In the embodiment in which prongs 26 are present onthe ends of wires 12, the prongs are solidly pressed and embedded intothe vessel wall 30 under the force of the balloon. The balloon is thendeflated and removed. If this installation technique is used, the wires12 do not need to be spring-biased outward; the force of the balloonwill press them outward into contact with the wall 30.

The catheter 2 is removed from the blood vessel by first removing theheat shrink Teflon™ tubing 32 or other structure which secures theproximal ends 34 of the wires. Each wire 12 is then withdrawn fromcontact with the blood vessel wall 27 into its respective guide tube 38.FIG. 2B shows the wires in this partially withdrawn position. Each wire12 is withdrawn until the loops 25 and prongs 26 are retracted into thesoft silicon rubber that forms tube 4 and guideways 38. Afterwithdrawing each wire 12 into its respective guide tube, the catheter iswithdrawn from the blood vessel using standard catheter withdrawalprocedures. The ability to withdraw the prongs 26 and loops 25 into theguideways 38 reduces damage to the blood vessel upon removal of thecatheter.

FIG. 3 shows the distal end of a second embodiment of the presentinvention. The second embodiment comprises a tube 41 with an ellipticalcross section and two lumens 42 and 44 that run the length of thecatheter. The second embodiment is intended to be used for hemodialysisapplications in which one of the lumens is used to aspirate blood andthe other lumen is used to infuse blood after dialysis. As in the firstembodiment, four positioning wires 50 extend the length of the catheterwithin guideways 52. In the second embodiment, two of the wires 50 arelocated along the major axis of the elliptical tube 41 while the otherwires are located along the minor axis. In this embodiment, the twowires 50 located along the major axis may extend from the tube 41 at adifferent angle than the two positioning wires which are located alongthe minor axis. Each wire 50 has a loop 54 and tip 56 near its end. Thetips 56 serve as penetration means for penetrating the wall of the bloodvessel, while the loops 54 serve as limiting means for limiting thedepth to which the tips 56 penetrate.

FIG. 4 shows the distal end of a third embodiment of the presentinvention. The third embodiment has four positioning wires 60 attachedto the distal end 62 through the use of securing hoops 64 and heatshrink Teflon™ tubing 66, which is placed over the hoops and shrunk intoplace. The combination of the securing hoops 64 and Teflon™ tubing 66helps ensure that the hoops 64 and wires 60 are securely attached to thedistal end 62 of the catheter. In an alternate embodiment, not shown,the wires 60 could be integrally formed into the catheter, thuseliminating the need for securing hoops 64 and tubing 66.

The positioning wires 60 extend radially outward from the securing hoops64. The wires 60 may be attached to securing hoops 64 by welding,brazing or other appropriate means. In some applications, it may bedesirable to treat the wires 60 with an antithrombotic coating to reduceblood clotting on the wires, as explained for the first embodiment. Eachwire 60 has a loop 68 formed near the end of the wire, such that a shortpenetration tip 70 extends outwardly from each loop. The prongs 70 serveas penetration means for penetrating the wall of the blood vessel, whilethe loops 68 serve as limiting means for limiting the depth ofpenetration.

This third embodiment of the antistenotic intravascular catheter isinserted into a patient's blood vessel using the same process asdescribed for the first embodiment. Although the third embodiment isstructurally simpler than the first embodiment, it requires a morecomplex procedure in order to remove the catheter from the patient'sblood vessel. The third embodiment may be removed using a proceduresimilar to the catheter insertion procedure described in the firstembodiment. A tubular introduction sheath of the type shown in FIGS.22-24 is placed over the catheter at the location where the catheterenters the blood vessel, and is subsequently slid down the catheteruntil it reaches the distal end of the catheter. The tubularintroduction sheath slides over the positioning wires 60, withdrawingthe loops 68 and prongs 70 from contact with the wall of the bloodvessel. After withdrawing the loops and tips into the introductionsheath, the catheter is slid within the introduction sheath andwithdrawn from the blood vessel. The introduction sheath could beremoved during or subsequent to removal of the catheter from thepatient's blood vessel.

FIG. 5 illustrates a tip retainer 9 at the distal end 8 of the catheterconstructed according to an alternative embodiment for retaining thecatheter tip within the blood flow stream and preventing the tip fromcontacting the inner wall 27 of the blood vessel 30. According to thisalternative embodiment of FIG. 5, the tip retainer 9 includes wires 72having a blunt terminating end 74 for contacting the inner wall 27 ofthe blood vessel 30. The blunt end 74 does not include a sharp tip ofthe type previously described with respect to tips 26, 56 and 70.Instead, the blunt end 74 contacts the inner wall 27 but does notpenetrate the wall of the blood vessel 30. The four wires 72 act toanchor the tip of the catheter with respect to the blood vessel wall andretain the tip within the flow in the blood vessel while preventing thetip 8 from contacting the blood vessel wall with the advantages aspreviously described. The wires 72 are prestressed to be resilientlyspring biased outward with an equal pressure from each of the wires 72such that the tip 8 is generally centered within the blood vessel 30.

An indexing mark 76 is also included on the catheter tube 4, extendingalong the length of the catheter tube 4. The indexing mark 76 visuallyindicates to a user the rotational orientation of the tip 8 within theblood vessel and thus indicates the rotational orientation of the tipretainer assembly. The position of the indexing mark 76 may indicate,for example, that the rotational orientation of the tip 8 is such thatone of the wires 72 is positioned where two of the blood vessels jointogether and is not contacting any wall of the blood vessel or providingstabilization. The user may then elect to change the rotationalorientation of the tip 8 such that each of the wires 72 is firmly incontact with the blood vessel wall. This visualization could also bedone, for example, with the catheter positioned within the introducersheath.

However, one reason for providing at least three and more preferablyfour wires 72 is because contact with three wires is generally deemedsufficient to stabilize and retain the tip 8 such that it does notcontact the wall 27. For example, the catheter 4 having the inventivetip retainer at the distal end 8 may be positioned at or near thebrachial cephalic junction and there is a likelihood that one or more ofthe wires 12 may fall into the junction. One advantage of havingmultiple wires is that the tip 8 can be stably anchored even if one ofthe wires is not anchored to the wall because the other wires will holdit in position. Thus, even if one of the wires 72 is not contacting theblood vessel wall because it is positioned in or along the junction, theother wires 72 will be contacting the wall and will retain the tip 8 ina position to prevent it from repeatedly bumping against the inner wall27 of the blood vessel 30.

FIG. 6 illustrates an alternative embodiment for the tip retainer 9having wires 78. The wires 78 include enlarged loops 80 at their distalend. The enlarged loops 80 do not penetrate the blood vessel wall 30.Instead, they rest firmly against the inner wall 27, as an anchor tofirmly retain the tip 8 in a fixed position within the blood vessel. Theloops 80 have an enlarged surface area to ensure that the blood vesselwall is not penetrated while providing a firm support for the tipretainer 9. The loop 80 abuts firmly against the inner wall 27 withoutpenetrating it in a manner similar to the anchor of a ship resting onthe sea bottom but not penetrating through the sea floor. The tipretainer 9 in this way anchors the tip 8 without penetrating the wall ofthe blood vessel 30.

FIG. 7 illustrates an alternative embodiment of the tip retainer 9having wires 82 formed in an enlarged loop 84. The loops 84 are formedfrom a single piece of wire that is bent at the end and terminates bybeing contacted to itself at the end 87, a single wire being within theguideway. Alternatively, the loop 84 is formed from the wire 82 beingbent in half and having two sections of the wire 82 extend within theguideway 86. The two ends of the wire 82 extend out of the proximal endof the tube 4 at position 34 as shown with respect to FIG. 1. The wires82 can therefore be extended or retracted, according to the user'spreference, to provide loops 84 of a desired size and shape. The wiresof the loops 84 are prestressed or bent to be resiliently spring biasedoutward so they extend with equal force and equal distance from the tip8 so as to retain the tip 8 in approximately the center of the bloodvessel 30. Use of loops 84 provides the advantage of broad contact area85 with the inner wall 27 while ensuring there is no penetration of thewall. The broad contact area at a distal region of each of the loops 84is a further aid for centering the tip 8 and ensuring that it is firmlyretained within the blood flow and the blood vessel and does not contactthe inner wall 27.

FIG. 8 is an alternative embodiment generally along the lines of FIG. 7with the loops 84 formed in a cloverleaf arrangement. The cloverleafshape of the wires 84 serve to further increase the contact area andprovides strength in anchoring the tip 8 of the catheter 4 within theblood vessel but without penetrating the wall of the blood vessel. Inone embodiment, the loops exit from the tip region 8 a selected distance95 back from the end of the tip. Having the wires exit spaced apart fromthe tip end 120 decreases the risk of creating blood clots at the end120 or forcing the lumen shut at the face 120 under a heavy spring forceby the wire loops 84. The end region 8, particularly the face 120, maybe constructed of a somewhat stiffer material to keep the lumen openingfrom being partially closed when the wire loops 84 are deployed.

In the cloverleaf arrangement of FIG. 8, each end of one wire extendsdown its own guideway 86, or alternatively multiple wires may extenddown the same guideway 86, permitting user manipulation of individualwires. The wires may exit from the face 120 of tip 8, or, as shown, exitfrom a location along the sidewall and extend forward, toward the tip.

FIG. 9 illustrates an alternative embodiment for the tip retainer 9 of athree-leaf clover configuration. Three loops 89, 91, and 93 are providedthat extend out of the surface of tip end 120 if desired. The threeloops 89, 91, and 93 are positioned equidistant around the catheter tube4. Using three wires provide the advantage of fewer wires in the bloodflow, but still produces sufficient force for anchoring. For example, aspreviously discussed with respect to FIG. 5, the catheter may beinstalled such that the tip is at or near the brachial cephalicjunction. Even if one of the loops 89 falls into the junction itself,the other two loops 91 and 93 will contact the wall and provide a stablecontact to anchor the tip 8 within the vessel. The term anchor is usedin this embodiment and all others herein in the broad sense of providinga general positioning of the catheter in the blood vessel. Some slightmovement from side to side or back and forth is permitted by the varioustip retainers as they anchor the tip 8 to the wall, just as a ship'sanchor permits some ship movement but holds it generally in position.

The wires 82 of loops of FIGS. 8 and 9 are formed with a preselectedresilient bias outwards as determined by their shape and construction.In some embodiments, a very light spring action is provided by having alight, resilient bias outward so that the device may be used in a widerange of size of blood vessels, from very small to very large, withassurances that the blood vessel wall will not be penetrated. In theembodiment of FIGS. 8 and 9, the spring bias force outward is easilyadjusted by varying the angle of connection between the straight portionwithin the guideway and the loop portion 84. For example, the angle atwhich the straight portion 83 extends from the tip 8 can be selected ata desired angle.

One distinct advantage of the present invention over the prior art isthat the catheter end 8 is retained within the flow of the blood andprevented from contacting the wall of the blood vessel without holdingthe catheter end 8 absolutely rigid. According to some prior arttechniques, such as that described in the article of Pieper, asdiscussed in the background of the invention, the concept is to hold thetip as rigid as absolutely possible. While this may have some benefit insome embodiments, one distinct advantage of the present invention isthat the invention will still operate properly even if the tip ispermitted to move to different locations within the blood vessel. Forexample, the tip 8 may move to one side or the other within the bloodvessel, based on movement of the patient, or of a rubbing of the bloodvessel. Additionally, the tip 8 may move longitudinally, along thedirection of the blood flow as the blood pulses. This is desirable inmany embodiments and may actually act to relieve some of the stresscreated by the presence of the catheter. The tip retainer 9 includesmembers having a light spring force which permits some relative movementbetween the catheter tip 8 and the wall 27 of the blood vessel. However,the springs have sufficient force that the catheter tip rarely actuallycontacts the blood vessel wall, thus preventing damage to the bloodvessel wall. In some of the embodiments described herein, the springforce becomes stronger as the catheter tip approaches the wall, thusserving to maintain the catheter tip in a spaced relationship from thevessel wall, even if some force is acting on the catheter tip 8 to pushit toward the wall. The light spring force at an extended location ofthe spring permits some catheter tip movement, but as the catheter tipbecomes closer to the wall, the spring force gradually increases, makingit more difficult for the catheter tip to actually contact the wall. Insome embodiments disclosed herein, the spring force is sufficientlystrong that as the catheter gets extremely close to the wall, it isforced back with significant pressure to prevent an actual impact withthe wall.

As will be appreciated, the tip retainer assembly 9 of each of theembodiments described herein may be made of or coated with anappropriate antithrombotic material that does not cause an adversereaction when placed within a patient's body, as previously described.

The physician extends or withdraws the wires in the embodiments of FIGS.1-9 to contact the blood vessel wall with the desired force. If thevessel wall has a large diameter, the wires are extended further.Similarly, if a high retaining force is desired, the wires can beextended slightly farther. On one hand, if the physician encounters asmall vessel, or one in which a weak retaining force is sufficient toanchor the tip 8, he may withdraw the wires as necessary.

The physician also selects a catheter tip having a properly sized andspring biased tip retainer assembly 9 for his intended uses. If thespring force is found to be too weak, or alternatively, too strong, hemay select another tip that is manufactured having a tip assembly 9 of aslightly different spring force, as necessary. (This may be done foreach of the embodiments described herein, as desired.) Similarly, arange of loop sizes and shapes is provided to permit the physician toselect the one that best suits the needs of a particular use.

The physician may observe the placement and operation of the cathetertip inside the blood vessel to ensure that it is properly anchored asthe procedure progresses. This observation can be carried out with knownultrasonic imaging equipment, for example. Alternatively, the tip 8 mayhave a radioactive isotope or other marker placed therein to permit thephysician to ensure that the tip is immobilized and not contacting thevessel wall. A fluoroscope or X-ray device may also be used to image thetip.

Often the tip must be in position in the blood vessel for an extendedperiod. Solid placement of the tip in a position which is spaced fromthe wall and securely anchored with respect to the wall followed byconfirmed observation of this by a physician is thus helpful to permitlong-term placement of the catheter without injury to the blood vessel.

FIGS. 10A and 10B illustrate a further alternative embodiment of theinvention. According to this alternative embodiment, an intravascularstent 154 is provided at the distal tip 8 of the catheter 4 for theprevention of stenosis and subsequent catheter occlusion. The stent 154is an intraluminal vascular prosthesis constructed of braided stainlesssteel, or other materials. They are, of course, coated with theappropriate materials to prevent interaction with the blood. Currentapplications of a standard stent include placement in the urinarysystem, and more recently, within arteries for arterial and coronarydisease as an intraarterial wall support usually following balloonangioplasty.

To deploy the stent according to the invention, an expandable balloon162 is positioned near the tip region 8 along the outer wall of thecatheter 4, or alternatively, a rolling membrane is provided around thestent 154 and constructed near the catheter tip. The balloon 162 iscovered with the self-anchoring stent 154, the entire assembly beingattached along the sidewall of the catheter tube 4 when it is insertedinto the blood vessel. After the catheter 4 has been inserted into theblood vessel with a tip 8 at the desired location, the balloon 162 isinflated to deploy the stent 154. The stent 154 includes prongs 163 thatpenetrate the wall of the blood vessel to solidly affix the stent 154and the catheter end 8 to the wall of the blood vessel. The balloon 162is then deflated. The stent 154 is connected to the catheter tip 8 byone or more anchoring wires 156, 158, and 160. If desired, to facilitatecatheter removal, the prongs 163 may be connected to the stent 154 withprestressed breakaway points so that they may be easily broken off andthe stent 154 removed. The prongs 163 may be composed of a materialwhich is absorbed by the body over time. Alternatively, the wires 156,158, and 160 which connect the tip 8 to the stent 154 may haveprestressed breakaway points at the surface of the stent, interfacingbetween the catheter and the stent 154. The catheter 4 may be removed bywithdrawing it, applying pressure to sever the prestressed breakawaypoints near the surface of the stent 154. In this embodiment, the stent154 remains within the body and, is preferably constructed of a materialwhich can be absorbed by the body over time rather than beingconstructed of stainless steel. Materials which can be absorbed by thebody are well known in the art and any of those which is commonly knownis acceptable for use to construct stent 154 or prongs 163.

According to the embodiment of FIGS. 10A and 10B, the stent 154 ispreferably a braided mesh, or an alternative embodiment, includes a slitextending longitudinally along its entire length. Having a slit in thestent 154, or alternatively constructing it of a braided materialpermits the stent to be completely collapsed, in a tight position aroundthe catheter 4 and then expanded by balloon 162 to have enlargeddiameter along the inside surface of the blood vessel.

By using the techniques according to the concept of this invention, asdisclosed in FIGS. 10A and 10B, as well as all other figures of thisinvention, the catheter tip 8 is anchored, preventing damage to theblood vessel wall and thus preventing cellular proliferation andstenosis.

FIG. 11 illustrates a further alternative embodiment of the catheterhaving a tip retainer 9 at a distal end thereof composed of fletching100. The fletching 100 is positioned adjacent to the tip 8 or, in oneembodiment, recessed back from the tip portion 8 a slight distance asshown in FIGS. 15 and 16 and explained in more detail herein.

An advantage of the use of fletching 100 is that the tip retainer 9 isconstructed in which the fletching 100 is a plastic or polymer which isinjection molded. In one preferred embodiment, the fletching 100 isinjection molded or extruded simultaneously with the injection moldingor extruding on the tube 4 so that the manufacturing cost is minimizedand the entire assembly is provided as a single, unitary member.

FIGS. 12-14 illustrate alternative embodiments for the shape of thefletching 100 which provides the tip retainer assembly 9. According tothe embodiment of FIG. 12, three fletchings are provided, 102, 104 and106. The fletching 100 is composed of the same material as the tube 4,being constructed from a unitary member in a preferred embodiment. Inthe embodiment of FIG. 12, the fletching 102 contains a flat surfaceregion 108. The flat surface region 108 extends circumferentially alongthe same radius of the catheter 4. That is, the flat surface 108 facesupward, presenting a planar surface generally at a tangent to thecircular catheter 4. The fletching 102 then extends upward, away fromthe tip portion 8, narrowing to terminate in a tip region 110. Thefletching 102 has a preselected resilient spring bias outward as itextends upward from a base region 112 towards the tip region 110. Thetip region 110 contacts the wall of the blood vessel but does notpenetrate the wall. The contact at the tip 110 performs the function ofanchoring the tip 8 with respect to the blood vessel wall so that thetip 8 is retained in a fixed position with respect to the blood vesselwall, without contacting the wall and remaining within the blood flow.In a preferred embodiment, three fletchings are provided, 102, 104 and106, each constructed similarly to that which has been described indetail with respect to fletching 102 and each providing a similar springbiased force outward to center the tip portion 8 within the bloodvessel.

According to the embodiment as shown in FIG. 12, the tip portion 110 ofeach of the fletchings 102, 104 and 106 is positioned beyond the end ofthe tip region 8, so that the anchoring position is beyond the distalend of the tip portion 8. Providing fletchings 102, 104 and 106 thatextend beyond the tip 8 is easily provided during the manufacturingprocess during the molding or extruding of the tubing 4, oralternatively by cutting the tip short after the extruding process sothat the tip 110 extends beyond the end of the tip 8.

In an alternative embodiment the fletchings 100 are positioned such thatthe tip portion 110 of the fletching 102 that contacts the blood vesselwall is approximately at the end of the tip portion 8 as explained withrespect to other alternative embodiments herein.

FIG. 13 shows an embodiment in which a fletching 114 has a flat planarportion 116 in generally the same orientation as the planar portion 108of fletching 102. That is, the fletching extends flat with respect tothe tubing 4, generally in the same circumferentially extending radiusas the tubing 4. However, the fletching 114 has a rounded tip portion118 providing a broader contact surface for anchoring the tip region 8with respect to the blood vessel wall. The broad surface area 118provides a large contact surface area to ensure that the tip portion 8is firmly retained in the desired position, spaced from the wall aselected distance at all times. Three fletchings are provided similar tofletching 114, spaced equidistant around the tubing 4.

FIG. 13 also illustrates an embodiment in which the contacting portion118 terminates prior to the end 120 of the tip portion 8 of the cathetertubing 4. In some embodiments, having the contact location to the bloodvessel wall approximately aligned with or slightly behind the actual tip120 of the tip portion 8 provides advantages in the operation andstructure of the device.

FIG. 14 illustrates an alternative embodiment for fletchings 100illustrating individual fletchings 122, 124 and 126. According to theembodiment of FIG. 14, the fletching 122 extends perpendicular to thecatheter tubing 4. That is, the fletching 122 is vertical with respectto the catheter tube 4, like feathers on an arrow. As best shown in FIG.14, in this embodiment the fletching is formed in a shape which curvesquickly upward, and extends in a generally straight, long tapered edge127 for an extended distance. The thin edge 127 contacts the inter wall27 of the blood vessel, to anchor the tip portion 8 at a selectedposition with respect to the blood vessel wall. The fletching has anextended contact edge along the blood vessel wall, to more firmly retainthe tubing 4 in a desired angular orientation and prevent rotation ofthe tubing 4. (This same advantage is provided by selected shapes of thewires of FIGS. 1-9 as well.)

In one embodiment, the fletching 100 is relatively stiff, so as toslightly stretch the blood vessel and at the particular point of contactcreate a slight depressed channel in which the fletching rests to anchorthe catheter. Preferably, the fletching is not so stiff as to penetratethe wall of the blood vessel but, is sufficiently stiff to preventexcessive undesirable rotation of the tip 8. The upper edge 127 may alsobe tapered to be thinner in cross section than the lower edge 130 ifdesired, as explained in more detail with respect to FIGS. 18 and 19herein.

FIGS. 15 and 16 illustrate an alternative embodiment in which the tipretainer 9 is composed of fletchings 132, 134 and 136 very much like thefletchings on an arrow. That is, as explained specifically with respectto fletching 132, the fletching has a long, tapered region 138, arounded upper region 140 and a rounded end or tip region 142. Just likethe fletching on an arrow, the fletching 132 extends vertically awayfrom the tube 4, perpendicular to the catheter tubing 4, similar to thedirection of orientation of fletching 122 of FIG. 14.

In the embodiment of FIG. 15, the fletchings 132, 134, and 136 arespaced a selected distance 137 from the end 120 of the tip portion 8.The rounded upper portion 140 contacts the blood vessel wall spaced aselected distance from the tip portion 8, as illustrated in FIG. 15. Inthe embodiment of FIG. 16, the fletchings 132, 134 and 136 arepositioned such that the rounded upper portion 140 is positionedapproximately aligned at the end 120.

An advantage of the embodiment of FIG. 15 is that the flow at thecatheter end 120 is not obstructed, interfered or altered by thefletchings 132, 134 and 136. Rather, the blood flow is affected only bythe presence of the tip portion 8 which can be configured alongconventional lines as known in the art to achieve a desired purpose. Thecontact to the blood vessel walls by the rounded portion 140 issufficiently close to the tip portion 8 that the tip portion is retainedwithin the blood flow and is prevented from contacting the blood vesselwall.

On the other hand, in the alternative embodiment of FIG. 16, having therounded portion 140 approximately aligned with the end 120 provides afirm control exactly at the tip 120 to ensure the maintaining of the tipportion 8 at a fixed location within the blood vessel at all times. Theend 120 is exactly anchored in position and undergoes little or nomovement because the anchor locations around the blood vessel wall aredirectly aligned with the tip end 120. This provides a firm positioningsystem for the tip portion 8 to ensure that the end 120 does not contactthe blood vessel wall, even under agitated conditions.

It is contemplated, for example, that in one embodiment a thin wire 139,such as the type shown in FIG. 17A, could be positioned along thetapered edge 138 and along the rounded edge 140 if desired for ensuringthat the rounded tip portion 140 always has sufficient spring bias toperform the anchoring function, even in a large blood vessel, and yethave the fletching sufficiently thin for an extended length that it canroll over, providing the improved characteristics of an increasedsurface contact area if desired.

FIG. 17B illustrates a further alternative embodiment for the fletchingin which an aperture 143 extends through the fletching. The fletching isthus a ridge of material having a top edge 140. The aperture 143provides an additional opening for blood flow while the ridges firmlyretain the tube 4 within the vessel. The size and shape of the aperturecan be varied to alter the spring strength, as desired.

FIGS. 18 and 19 illustrate a particular advantage of the fletchingaccording to the present invention. The fletching is tapered as itextends outward. That is, the fletching is relatively thick at the base144 where it extends from the tubing 4 and tapers to a very thin edge atthe outside regions, particularly at region 140. Having the fletchingtapered provides the advantage that one size fletching will fit allblood vessel sizes within a selected range.

For example, as best shown in FIG. 18, the catheter 4 is in a relativelylarge blood vessel the fletchings 132, 134 and 136 extend straight, andinto contact with the blood vessel wall 27. The tip of the fletching 140may roll over slightly, depending upon the size of the blood vessel. Thesize of the fletching 132 is selected to ensure that it will at leastcontact the inner wall 27 of any blood vessel into which it is to beused so that it may perform the tip retaining function as has previouslybeen described. However, in a large blood vessel, such as the type shownin FIG. 18, the tip 140 may slightly contact the edge, thus providing anadequate anchor surface area to retain the catheter tubing 4 in a fixedposition as has been described.

FIG. 19 illustrates a smaller blood vessel and the same tip retainer asused in FIG. 18 herein; the fletching is rolled over at the edges, in abroad circumferential contact with the blood vessel wall 27'. The edge140 can easily roll over and be positioned along the surface of the wall27' without taking up significant blood vessel area while providing arelatively large contact surface within a small blood vessel. Thetapering of the fletching and providing it with thin edges at 140provides the advantage that even in a small blood vessel, the samefletching may be used except that a larger surface area of the edgeportion of the fletching 140 will be in abutting contact with thesurface of the wall. This provides the additional advantage ofincreasing the cross-sectional area of contact between the fletching andthe blood vessel, to more securely retain the tip portion 8 within thecentral region of the blood vessel and prevent contact with the wall27'.

The tapered fletching provides the additional advantage that a preformedtip assembly 9 can be used in many sizes of blood vessels. A singleblood vessel may have a large inner diameter lumen at one region and asmall inner diameter lumen in a different region. The difference indiameter may be caused by localized thickening of the walls, injury,fatty build up, or other causes. When the catheter is placed in thevessel, the physician may not be aware of the exact diameter of theblood vessel at the desired location (even though it might be measuredultrasonically, for example). The physician is assured that the cathetertip will be properly retained in the blood flow and spaced from the walleven if the exact dimensions are not as was expected at the installationsite. (This advantage is provided in other embodiments also, such as theembodiments of FIGS. 1-9 by the selective withdrawal or extension of thewires, as previously explained.)

Having tapered edges provides another distinct advantage: the relativeflexibility and spring bias within the fletching may be easily alteredalong the fletching as it extends outward. That is, at the very edge ofthe fletching near rounded portion 140, the resilient bias can be verylight because the fletching is very thin at the edges. Closer to thebase, the fletching gradually becomes thicker, naturally increasing thespring strength and resilient bias within the fletching. This has theadvantage of increasing the centering ability of the tubing 4 because ifthe tubing begins to be pressed out of position, towards one wall thefletching on that side of the tubing will have the base region pressedcloser to the wall; however, the base region being thicker and having astronger spring action will tend to increase the resilient bias awayfrom the wall to push with more force away from the wall and tend tocenter the tubing 4 within the blood vessel. Each of the fletchings areconstructed with uniform spring bias to act together in generallycentering the tubing 4 within the blood vessel and prevent the tubingfrom becoming too close to the blood vessel wall on any side.

In one embodiment, the spring strength of the fletching variesproportional to the thickness of the fletching. In an alternativeembodiment, the fletching is constructed such that the spring bias isnot uniform with respect to the thickness of the fletching. For example,a relatively strong spring bias can be placed adjacent the base, evenmore than would otherwise be present, to ensure that the tubing 4 isalways spaced at least a minimum distance from the wall 27.Alternatively, a slightly stronger spring bias may be placed right atthe tip 140 than would otherwise be present based on the edges beingextremely thin because the edges may be so thin as to have little or nospring bias based on their own thickness. In such an embodiment, theproperties of the material or the type of material used may be slightlyaltered at the very tip region 140 to provide sufficient spring strengthto anchor the end even though the tip portions are extremely thin.

FIGS. 18-21 also illustrate alternative embodiments for the orientationof the fletching on the tubing 4. According to one alternativeembodiment as shown in FIGS. 18 and 19, the fletching is straight,directly in line with the tubing 4. This is the same style for mountingthe fletching on some arrows, as is known in the prior art.Alternatively, the fletching may be mounted at a cant to provide aspiraled fletching as best shown in FIGS. 20 and 21. When the fletchingis mounted at a cant, so as to slightly spiral around the tubing 4 thisprovides the advantageous effect of smoother blood flow through theblood vessel while aiding to maintain the tip 4 in a straight-lineorientation with respect to the blood vessel.

The fletching as illustrated in FIGS. 12-21 has the advantage of beingeasily constructed. In one embodiment, the molding 4 and fletching isconstructed as an integral piece by injection molding methods known inthe art. The material can be constructed from a polymer, silicone, orany other well-known nonthrombogenic material. Alternatively, the tubing4 can be extruded with the fletching being provided in an extrusion moldprocess. Another advantage of the fletching is that it permits easysheath removal and insertion, as will be explained later in more detail.The fletching also is easily constructed with graduated stiffness alongthe length of the fletching as it extends away from the tubing 4providing the advantages previously described.

The insertion and removal of the catheter tubing 4 having the tipretainer on the end thereof will now be explained in particular detailwith respect to FIGS. 22-24. The description of FIGS. 22-24 isparticularly directed towards an embodiment having loops generally ofthe type previously described with respect to FIG. 9; however, this isfor illustration purposes only and the same or similar method ofinsertion and removal is uniformly applicable to each of the embodimentsdescribed herein.

Referring now to FIG. 22, the catheter 4 having the tip retainer 9 atthe end thereof is prepared for introduction into the blood vessel byplacing it within an introducer sheath 148. The introducer sheath 148 ispreferably made of polyurethane, plastic or some other relativelypliable material that is sufficiently stiff to overcome the spring biasof the retainer member so that the entire assembly has a diameterapproximately equal to that of the catheter tubing 4. The introducersheath 148 includes a handle portion 150 which the physician may use tomanipulate the introducer sheath 148 and guide it into the properposition within the blood vessel. In a preferred embodiment, theintroducer sheath 148 has a slight taper 152 at the distal end to makethe introduction into the blood vessel more simple.

As shown in FIG. 23, the introducer sheath is advanced into the bloodvessel 30 until the catheter tube is at the desired location within theblood vessel. At this position, the tip retainer 9 is held within theintroducer sheath and does not contact the wall of the blood vessel 30.

As shown in FIG. 24, the introducer sheath 148 is then removed from thecatheter tubing 4. According to a preferred embodiment, the introducersheath 148 is constructed of a relatively thin layer of polyurethanewhich is easily ripped or torn by the physician. In order to remove theintroducer sheath, the physician firmly grabs the handles 150 on eitherside and begins to tear apart the introducer sheath. The introducersheath will separate into two pieces, tearing apart outside of the bloodvessel and withdrawing the introducer sheath from the catheter tubing 4.As the introducer sheath is withdrawn from the catheter tubing 4, thetip retainer is released and automatically extends outward according tothe preset spring bias to contact the blood vessel wall and retain thetip portion 8 at the selected location as has been previously described.

In an alternative embodiment, the sheath is simply removed by sliding itbackwards, rather than tearing the sheath into two pieces. As will beappreciated, tearing the sheath into two separate pieces provides thedistinct advantage of permitting the introducer sheath to be easilyseparated from a portion of the tubing without having to completelyslide off the end of the tubing outside the body. It also provides theadvantage that the physician may easily and uniformly withdraw theintroducer sheath while leaving the tubing 4 in the preset position, topermit the tip retainer to be deployed to retain the tip portion 8 inthe desired position within the blood vessel.

Removal of the catheter 4 having the tip retainer 9 on the end thereofis easily accomplished with each of the alternative embodiments. In thealternative embodiments of FIGS. 5-21, it will be appreciated that thetip retainer does not penetrate the blood vessel wall 27. Further, inmany of these embodiments the tip retainer is constructed to permit easywithdrawal or removal from the blood vessel. According to one method ofremoval, the catheter 4 is simply withdrawn from the blood vessel, andsimultaneously withdraws the tip retainer while in the deployedposition. Even though the tip retainer is deployed, such is shown inFIGS. 8 and 9 and others, the orientation is such that the withdrawalmay be easily accomplished because the spring bias permits the tipretainer 9 to be pressed inward slightly as necessary. To advance thetip retainer would be difficult, or impossible, because this would serveto increase the spring bias and press the tip retainer 9 more firmlyinto position against the blood vessel wall, increasing the anchorstrength. On the other hand, the withdrawal of the catheter tube 4 tendsto pull the tip retainer 9 away from the wall and permit easy removalwithout excessive stress on the blood vessel wall.

According to an alternative embodiment, the tip retainer is withdrawnfrom the deployed position so as to not contact the wall by sliding anintroducer sheath once more over the tip portion 8 to withdraw the tipretainer 9 from the blood vessel wall. The sheath and catheter tube 4may then be withdrawn from the blood vessel.

FIGS. 25 and 26 illustrate another preferred embodiment of the tipretainer 9 composed of a loop 168 according to principles of theinvention. In the embodiment shown in FIGS. 25 and 26 the tip retainer 9is comprised of a single loop 168 of wire 166 and silicone tubing 160having one end 162 and the other end 164 connected to the distal end.Inside the silicone tubing 160 is the stainless steel wire 166. Thesilicone tubing 160 with the steel wire 166 on the inside thereof formthe loop 168, which functions as the tip retainer 9.

The size of the loop 168 is selected based on the size of the bloodvessel and position placement of the catheter 4 in that blood vessel. Inone embodiment, the loop 168 has a diameter of 20 millimeters and theends 162 and 164 are connected to the tip portion 8 spaced from the tipportion 8 approximately 7 millimeters. In other alternative embodiments,the diameter of the loop 168 is considerably smaller, in order to beproperly sized for placement in the selected vessel of the human bodyduring a kidney dialysis or other procedure, as explained herein.

The ends of the loop 168 are fixed to the catheter 4 by any suitabletechnique including silicone adhesive, forming an incision in the tubing4 and insertion into this incision followed by sealing with siliconeadhesion, or the like.

The diameter and spring strength of the steel wire 166 is selected toprovide the desired spring force to urge the loop 168 to return to theround position as shown in FIG. 25. Generally, a relatively light springforce is acceptable as would be provided small diameter wire 166. Othermaterials besides stainless steel, such as various alloys of steel,spring steel, teflon coated steel, and the like are also acceptable. Thesilicone tubing 160 is provided as antithrombogenic coating which iseasily manufactured attached to the catheter 4. Any other acceptableantithrombogenic coating besides the silicone tubing 160 could also beused, such as the antithrombogenic coatings described with respect tothe other embodiments herein.

In one embodiment, the wire 166 is not present. Instead, only thesilicone tubing at 160 is used to form the loop 168 because the properspring constant is provided from the natural spring within the siliconetubing itself.

FIG. 27 illustrates the tip retainer of FIG. 25 positioned at onepossible location within the blood vessel 30 (the tip region 8 must bepositioned at a desired location according to the medical procedurebeing carried out). Preferably, the tip portion 8 is not adjacent ajunction 170 between two blood vessels 30 and 30' as shown in FIG. 27.To carry out many medical procedures the tip region 8 must be positionedat a desired location according to the medical procedure being carriedout. In some situations, either accidentally or by medical design, thetip region 8 may be adjacent a branch 170 between one blood vessel 30and another blood vessel 30' to guard against falling into the junction170, the diameter of the loop 160 is selected to ensure that the tipretainer 9 bridges the junction 170 so that the catheter 4 is anchoredwithin the blood vessel 30 and does not contact the walls of the bloodvessels 30 or 30'. Preferably, the diameter of the loop 168 is selectedsuch that when the catheter 4 is compressed within the blood vessel thatthe longitudinal length of the loop 168 denoted by the distance x inFIG. 27 is longer than the diameter d of a blood vessel which may form ajunction with the blood vessel 30'. By selecting a loop sized 168 suchthat the distance x larger than the diameter of any blood vessel 30' forwhich a junction 170 is expected to be encountered, the loop can beassured of adequately bridging the blood vessel at the branch 170 andstill have sufficient support from the main blood vessel 30 on eitherside of the walls 27 of the main blood vessel 30. For example, thedistance x can be in the range of 1.5 to 3 times the distance dsufficient support along the blood vessel wall 27 from the tip retainer9 that the tip portion is maintained in a central region of the vessel30. Of course, the distance x can be significantly longer than threetimes the diameter d, if desired and depending upon the diameter d whichis encountered at various locations within the blood vessel 30. Thedistance x may be somewhat larger than the diameter of the loop 168 inthe round position because as the loop 168 is compressed, the distance xincreases to provide an elongated contact position along the length ofthe wall 27.

The loop 168 is preferably constructed of a small diameter material,such as a silicone tubing having an outside diameter of 1 millimeter orless or a wire having an outside diameter of 0.5 millimeters or less.Using a small diameter material to construct the loop 168 provides theadvantage that blood flow through the main blood vessel 30 is notimpeded by the tip retaining member 9. If the tip portion 8 happens tobe positioned adjacent a junction 170, the additional advantage is thatblood flow into or out of the blood vessel 30' that junctions with theblood vessel 30 is not impeded by the loop 168 bridging the junction 170between the blood vessels. Even if the loop 168 is positioned directlyover the opening of 30' at the junction itself, the loop diameter issufficiently small that blood may easily flow through the blood vessel30' as needed.

The operation of the device of embodiments 25-27 is as follows. Thecatheter 4 is positioned in the blood vessel using any acceptabledelivery system. The delivery system of the type shown and describedwith respect to FIGS. 22-24 is acceptable. Upon being positioned withinthe blood vessel 30, the loop 168 becomes elongated by compression fromthe walls 27 of the blood vessel 30. The spring constant of the wire 166is selected to be sufficiently light that the loop 168 is easilycompressed by the wall 30 and exerts only a light force upon the innersurface. However, the spring force is sufficiently strong to engage theblood vessel wall 27 and prevent repeated contact between the tipportion 8 and the blood vessel wall 27.

At the conclusion of the medical procedure, the catheter 4 is simplywithdrawn by being retracted it while leaving the loop 168 in thedeployed position. Alternatively, a retraction sheath may be placedaround the catheter 4 which slides along the outer diameter of catheter4 and compresses the loop 160 to move it away from the wall of the bloodvessel similar to that shown in the introduction position of FIG. 23.The catheter 4 is then removed.

FIGS. 28A-28C illustrate alternative embodiments which have been founduseful for performing kidney dialysis. Preferably, for kidney dialysiscatheter 4 is a double lumen catheter having an inflow lumen 42 and anoutflow lumen 44. The tip portions 8 of the lumens are slightlystaggered to provide improved inflow and outflow characteristics forkidney dialysis. The attachment locations for ends 162 and 164 (notshown) are selected proximal to the outflow region 42 of one lumen withthe loop extending forward, beyond the tip of the in flow lumen 44. FIG.28A illustrates the embodiment in which the loop 168 is composed only ofthe silicone 160 and does not include an internal wire 166.

FIGS. 3, 28B and 28C illustrate alternative embodiments for the catheter4 [double lumen]. FIG. 23 illustrates a double lumen catheter with thelumens ride-by-ride. As shown in FIG. 28B, the catheter 4 can be adouble "D" lumen catheter having staggered tip portions for each of thelumens 42 and 44. The walls of the catheter 4 are solid walls formed ofany suitable material known in the art. The loop 168 is attached by anyacceptable technique, such as silicone adhesive, insertion into the wallof the catheter 4 or the like. FIG. 28C illustrates the embodiment inwhich the catheter 4 includes additional guideway lumens within the wallof the catheter 4. Specifically, lumens 172 and 174 are provided in acircumferential region of the catheter 4. The lumens extend along thelength of the catheter. The loop 168 extends from the lumens 172 and174, the lumens acting as guideways for the loop 168. The ends of thematerial that form the loop 168 may extend along the length off thecatheter 4 so that the loop 168 may be retracted and extended asnecessary. An additional lumen 176 is also provided in the central wallbetween the two lumens 42 and 44 for additional uses, if desired.

FIG. 29 illustrates a still further alternative embodiment instructedaccording to principles of the present invention. The loop 168 is formedby being rigidly attached at one end 162 to the tip portion 8 and havingthe other end 164 inserted into a lumen 178 of the catheter 4. In thisembodiment, the loop 168 includes a hollow silicone tubing 160 of thetype previously described. The wire 166 is within the tubing 160, oralternatively is not used, as desired. The other end of the loop 168extends into a lumen 178 within the catheter 4. The lumen 178 may be alumen of the type formed within a wall of the catheter or,alternatively, may be an extension of the silicone tubing 160 connectedalong the outside of the wall of the catheter 4 or embedded within thewall. In each structure, the lumen 178 provides an open passage way fromthe tip portion 8 to a proximal portion of the catheter 4, which isexternal to the patient.

The tubing 160 contains a plurality of apertures 180 spaced from eachother around the loop 168. In one embodiment, the apertures 180 areequally spaced from each other around the entire loop. Alternatively,the apertures 180 are positioned only along the side portions of theloop 168, which are anticipated to contact the wall 27 of the bloodvessel as shown in FIG. 27. The very tip region 182 of the loop does notcontain any apertures in this alternative embodiment.

Medication can then be delivered through the lumen 178, into the loop168 constructed from the hollow tubing 160 and exit the apertures 180for administration to the patient. The silicone tube 160 thus becomes amedication delivery system. When the catheter is positioned for anextended time within the human body, as may occur with kidney dialysis,it is known in the art that smooth muscle cell growth, plateletaggregation, and the like to deliver medication may occur. The use of atip retainer to deliver medication constructed according to principlesof the present invention minimizes occlusion of the blood vessel, andreduces destruction of the blood vessel by delivering specificanti-clotting agents to the tip region 8 via the apertures 180 in theloop 168. It is known in the art that the smooth muscle wallssurrounding the blood vessel are inhibited from excessive growth bycertain medications. One of the problems identified according toprinciples of the present invention and which the invention seeks toprevent is excessive growth of the smooth muscles around the bloodvessel wall which may overgrow into and cause occlusion of the bloodvessel 30. The medication delivery system as illustrated in FIG. 29 anddescribed herein advantageously delivers medication precisely to thelocation desired for inhibiting excessive growth of the muscle cellsaround the blood vessel wall and for inhibiting platelet aggregationalong the wall of the blood vessel or other clotting along the walls ofthe blood vessel. The medications which may delivered include TPA, ananticlotting agent; strepokinase, heparin, hirudin, or the like. In someinstances, clotting beings to occur along the walls 27 of the bloodvessel 30. The loop 168 is in actual contact with the blood vessel wall27. The medication can therefore be delivered directly to the wall ofthe blood vessel with benefits obtained in addition to those which maybe obtained by delivering the same medication exiting from the mainlumen 28 of the catheter.

The position, size and relative location of the apertures 180 areselected to provide the desired delivery medication. In someembodiments, having the apertures 180 spaced equidistance from eachother and opening to both the inside and outside of the loop 168 isdesirable to provide medication equally around the loop 168. In analternative embodiment, the apertures 180 are spaced only on an outsidesurface of the loop 168 to deliver the medication outward from the loop.In a further alternative embodiment, the apertures 180 are positionedonly at or near locations which are anticipated to come in contact withthe wall 27 of the blood vessel 30. The apertures 180 may be oriented todischarge the medication along the surface of the blood vessel wall 27and thus are radially offset from the outside position to deliver themedication adjacent the wall 27 so that the wall 27 does not blockoutflow of the medication.

Having the tubing 160 or, alternatively, a wire 166 within the tubing160 extend to the proximal end of the catheter 4 provides the additionaladvantage that the loop 168 may be retracted or extended as necessary.When the catheter 4 is inserted into the patient, the loop 168 can be ina retracted, small diameter position held tightly against the tipportion 8. Once the catheter is at the proper location, the wire 166, ifpresent, or alternatively the tubing 160, may be pushed along the lumen178 to enlarge the loop 168 to a size and shape as described withrespect to FIG. 27. The loop 168 thereafter remains in the extendedposition during the medical procedure. At the conclusion of the medicalprocedure, the wire 166, or alternatively the lumen 160, are retracteddown the lumen 178 to again reduce the diameter of the loop 168. Theloop 168 may also be retracted or extended using the lumens 172 and 174of the catheter of FIG. 28C. The catheter 4 is then withdrawn from thepatient. Alternatively, a delivery system of the type described withrespect to FIGS. 22-24 may be used and the loop 168 starting in thedeployed position and only being retracted for removal of the catheter4.

FIG. 30 illustrates a further alternative embodiment of the tip retainer9. According to the embodiment of FIG. 30, two triangular siliconestrips 182 and 184 are positioned adjacent the tip portion 8. The lengthx of the silicone strips 182 for combination with the angle θ withrespect to the wall of the catheter 4 are selected to cause therespective tip regions 186 and 188 to contact the walls of the bloodvessel 30 with light spring force to anchor the tip portion 8 to theblood vessel 30. The angle θ is also selected to be sufficiently smallthat if the tip portion 8 happens to be positioned adjacent a junction170 that the sides of the triangular member contact the walls 27 ateither edge of the junction 170 and prevent the tip portion 8 frombecoming sufficiently close to the wall adjacent the junction that itcontacts the junction itself or the wall adjacent junction. In the eventone of the triangular members 184 enters the blood vessel 301 atjunction 170, two contact points are advantageously provided instead ofthe single previous point 188, thus further increasing the stability ofthe anchoring of the tip portion 8. The number of triangular members182, 184 used depends on the particular application, and preferably 2, 3or 4 such triangular members are used.

The triangular members 182 and 184 include respective apertures 185. Theapertures 185 advantageously permit the spring constant of thetriangular members 182 to be selected by making the aperture small orlarge to provide a correspondingly large or small spring constant asdesired. Further, the apertures may also provide the benefit of thetriangular members 182 and 184 minimizing interference with the flow ofblood.

Constructing the triangular members 182, 184 from a strip of siliconeprovides the advantage previously described with respect to the loop 168that blood flow through the blood vessels 30 or 30' is not impeded withthe catheter 4 in position. Flow to or from the branch at the junctionis not restricted.

FIG. 31 illustrates an alternative embodiment for the tip retainingmember 9 comprised of triangular members 190 constructed from sheets ofsilicone. Preferably, the sheets are solid sheets of silicone which arerelatively thin, less than 1 millimeter, so as to not impede the bloodflow and yet be sufficiently strong to retain the catheter 4 anchored ina space position from the blood vessel wall 27.

FIGS. 33A, 33B and 34 illustrate an alternative embodiment for a tipretainer in the form of longitudinal strips 192 of silicone sheeting. Inthe embodiment of FIG. 33A, the tips 194 are rounded to reduce thetrauma in the blood vessel and spread the spring force over a greaterarea in the blood vessel. In the alternative embodiment of FIG. 33B, thetip portions 196 are pointed to concentrate the spring forces at asingle location and slightly deflect the wall 27 of the blood vessel atthe point of contact 196. Having a more pointed tip 196 increases theforce with which the tip member 9 is embedded into the wall 27 of theblood vessel and may be desired in some embodiments. In the embodimentsshown in FIGS. 33A, 33B and 34 two strips 192 of silicone sheeting areshown. However, it is contemplated that three or four strips may also beused spaced equidistance around the catheter 4 similar to that shown inFIGS. 12-21, if desired.

FIGS. 35 and 36 illustrate an alternative embodiment for the tipretainer 9 composed of two loops 198 and 200. The embodiment of FIGS. 35and 36 is particularly adapted to use on a catheter for having a doublelumen with the opening staggered as illustrated in FIGS. 36 and 28A.According to this embodiment, a first end 162 of each loop originatesnear the upper region 202 of the most forward tip of the catheter 4,extends outward, in a loop of the desired shape, and terminates at thebase region 204 of the opening of the other lumen where the other end164 is attached. The loops 198 and 200 are constructed from siliconetubing, silicone sheeting or alternatively, from a tubing having aspring wire therein of the type previously described with respect toFIGS. 25-27. The use of loops or loop having their terminated ends 162and 164 spaced longitudinally along the catheter may be used in theother embodiments of FIGS. 25-29 and is desired in some medicalprocedures to provide increased stability at different points along thetip portion 8 of the catheter 4.

FIG. 37 illustrates an alternative embodiment in which the catheteritself is modified to provide the tip retaining member 9. In thisembodiment, the tip portion of the catheter 4 is severed by an incisionalong the tip for a selected distance creating two halves, 206 and 208.A string, wire or other attachment device is connected to the ends 210and 212 respectively of the halves 206 and 208. The strings 207 and 209are then retracted a desired amount to form two loops 214 and 216 in theend of the catheter 4 similar to that shown in the embodiment of FIGS.35 and 36. The attaching members 207 and 209 are retracted the desiredamount to form the loops 214 and 216 of a selected size and shape. Aslight retraction of the attachment means 207 and 209 will cause theloops 214 and 216 to be relatively large and extend into solid abuttingcontact with the walls of the blood vessel. If the loop catheter 4 ispositioned in a smaller portion of the blood vessel, the attachmentmembers 207 and 209 can be further withdrawn, decreasing the size of theloops 214 and 216 to provide the desired spring bias force for retainingthe tip portion 8 within the blood vessel 30. The embodiment of FIG. 37provides the advantage of ease of manufacture because the catheteritself is modified to form the tip retaining member 9. Alternative tousing wires 207 and 209, if the size of the loops 214 and 216 ispreviously known, the tip portions 210 and 212 may be attached to theside wall of the lumen 4 by the appropriate adhesive to easily form theloops 214 and 216 having a desired size and spring constant. For thisembodiment, the attachment wires 207 and 209 are not necessary and loopssimilar to that shown in FIG. 35 can easily be formed by sacrificing aportion of the tip region of the catheter itself and using a cathetermaterial to form the loops 214 and 216.

FIGS. 38A and 38B illustrate an alternative embodiment for the tipretainer 9. A loop 219 constructed from any acceptable material havingthe desired spring constant is attached to the tip region 8 of thecatheter for using any one of the acceptable techniques describedherein. In addition, a retraction wire 220 is attached adjacent a tipregion 222 of the loop 219. The retraction wire 220 extends along thecatheter 4, either along the outside surface or through a lumen in itsposition near the proximal end for manipulation by a physician. The loop219 is formed with the shape such that the spring memory forces if intoan extended, elongated position while relaxed, such as shown in FIG.38A. Preferably, the loop 219 in the relaxed position will have a heighth approximately equal to that of the catheter for itself. After thecatheter 4 is advanced to the desired position of the blood vessel 30,the retraction wire 220 is retracted by the physician causing the loop219 to go outward and engage in abutting contact with the walls 27 ofthe blood vessel 30. The retraction line 220 is then secured at aproximal end in the catheter 4, outside the patient, and acts as a tipretainer deployment device to maintain the tip portion 8 of the catheter4 within the blood vessel. At the conclusion of the medical procedure,retraction line 220 is released which permits the wire 219 to return toits relaxed position as shown in FIG. 38A. The catheter 4 is thenremoved from the blood vessel. The loop 219 may be composed of a singleloop of material of the type shown in FIGS. 25-27, or alternatively, maybe composed of two or more loops in the form of an egg beater typepattern to provide multiple abutting contact points with the wall of theblood vessel when the retraction wire 220 is retracted.

FIG. 39 illustrates a further alternative embodiment at the tip retainer9 in which a circle 224 of silicone sheeting is affixed near the distalend 8 of the catheter 4 to form the tip retainer 9. The loop 224provides extended contact points with the blood vessel wall along itsentire length similar to that shown for the loop of FIG. 27. In theembodiment of FIG. 39, the loop 224 is positioned with its most forwardend adjacent the tip portion 8 and extending backwards, while in theembodiment of FIG. 27, the loop 168 extends forward from the tip portion8. Similar to the embodiment shown and described with respect to FIGS.25-27, the loop 224 may be composed of flat silicone sheeting, hollowsilicone tubing having a spring wire therein, or alternatively a springwire by itself coated with an antithrombogenic material.

FIG. 40 illustrates a further alternative embodiment at the tip retainermember 9 according to the present invention which includes vanes 226having a generally triangular shape. The shape of the vanes 226 areslightly different from the shape of the vanes 192 because they extendin a triangular shape from the catheter wall 4. The broader, triangularbase of the vanes 226 advantageously permits the strength of the vein226, and thus the spring constant to gradually increase towards the bodyof the catheter 4 while maintaining the same thickness for the vein 226as shown in FIG. 34. The particular shape of the triangle 226 isselected depending upon the desired location within the blood vessel toprovide the spring constant which maintains the catheter 4 at a spacedposition from the blood vessel wall at all times, even as may occur fromrepeated movement of the patient.

While the preferred embodiment of the invention has been illustrated anddescribed, it will be appreciated that various changes can be madetherein without departing from the spirit and scope of the invention.

What is claimed is:
 1. A catheter adapted for insertion into a bloodvessel having blood flowing therethrough, comprising:a catheter having adistal end, a proximal end, a tip and an internal passageway forpermitting fluids to pass through the catheter; and a tip immobilizingmeans located at the distal end of the catheter for anchoring the distalend of the catheter within the blood flow to maintain the tip of thecatheter in a spaced relationship from a blood vessel wall and toprevent the tip of the catheter from contacting a wall of the bloodvessel without substantially obstructing fluid flow of blood through theblood vessel, such that catheter failure due to stenosis or thrombosisat the catheter distal end if reduced.
 2. A catheter adapted forinsertion into a blood vessel comprising:a catheter having a lumentherein that permits fluids to pass through said catheter, the catheterhaving a tip portion and a proximal portion spaced form the tip portion;a tip retainer assembly attached to the tip portion of the catheter; anda plurality of wall contact members, each of which contacts a bloodvessel wall when the catheter is within a blood vessel, the wall contactmembers being a part of the tip retainer assembly, the wall contactmembers including a wall contact portion for contacting the blood vesselwall at a selected location and remaining in contact with the bloodvessel wall for an extended time, the wall contact members beingattached to said catheter tip portion and maintaining the catheter tip aspaced distance from the blood vessel wall and preventing the cathetertip from contacting the blood vessel to prevent damage to the bloodvessel wall by repeated contact between the catheter tip and the bloodvessel wall.
 3. The catheter according to claim 2 wherein each of saidwall contact members is spring biased with a selected spring force forextending into abutting contact with said blood vessel wall, each ofsaid wall contact members being spaced from each other circumferentiallyaround the catheter tip portion to provide a tip retainer assembly thatresiliently biases the catheter tip a fixed distance spaced from saidblood vessel wall and maintains the catheter tip within the blood flowregion.
 4. The catheter according to claim 2 wherein said wall contactportion contacts said wall at a position adjacent the tip of saidcatheter tip.
 5. The catheter according to claim 2 wherein said wallcontact members are spring biased for permitting the tip portion to movewithin the blood vessel for providing a spring bias force that preventsrepeated contact between the tip portion and the blood vessel wall toprevent damage to the blood vessel wall.
 6. The catheter according toclaim 5 wherein the wall contact members exert a light spring force forcentering the tip portion within the blood vessel wall when the tipportion is approximately in the center of the blood vessel and exerts agradually increasing spring bias force as the tip portion becomes closerto the wall, increasing the force with which the catheter tip portion isheld away from the wall as the tip portion comes closer to the wall, thelight spring force permitting relative movement of the catheter tip, andthe gradually increasing spring force making it more difficult for thecatheter tip to actually contact the wall.
 7. An assembly adapted forinsertion into a blood vessel comprising:a catheter means forintroduction into a blood vessel, the catheter means being adapted tobeing positioned within the blood vessel, the catheter means having atip portion; an introducer assembly means for aid in inserting the saidcatheter means into a blood vessel; and a tip retainer assembly meanslocated at the distal end of the catheter for retaining the tip portionin a relatively fixed position within a blood vessel, the tip retainerassembly means being adapted to be in a retracted position when thecatheter means is not positioned within the blood vessel and in adeployed position when the catheter means is within the blood vessel,the tip retainer assembly means retaining the tip portion of thecatheter means in a spaced position from the blood vessel wall andpreventing repeated contact of the tip portion of the catheter meanswith the blood vessel wall.
 8. The assembly according to claim 7 whereinthe introducer assembly includes a means for holding the blood vesselopen to facilitate positioning of the catheter means at a desiredlocation in the blood vessel.
 9. The assembly according to claim 8wherein said means for holding the blood vessel open includes anintroducer sheath means for enclosing the catheter means and for holdingthe blood vessel open.
 10. The assembly according to claim 9 whereinsaid introducer sheath means includes an introducer sheath removal meansfor permitting easy removal of the introducer sheath from the cathetermeans.
 11. The assembly according to claim 10 wherein the introducersheath removal means includes a tearable membrane which forms a tubularportion of the introducer sheath for enclosing the catheter means andgripping means for gripping the introducer sheath, while tearing theintroducer sheath to the introducer sheath from the catheter means. 12.The assembly according to claim 7 wherein said tip retainer assemblymeans includes a spring means for permitting the tip portion to move alimited distance within the blood vessel but for providing a spring biasforce that prevents repeated contact between the tip portion and theblood vessel wall to prevent damage to the blood vessel wall.
 13. Theassembly according to claim 12 wherein the spring force provided by thespring means increases in strength as the tip portion becomes closer tothe blood vessel wall, thus serving to maintain a spaced relationshipbetween the blood vessel wall and the tip portion.
 14. The assemblyaccording to claim 12 wherein the spring means exerts a light springforce for centering the tip portion within the blood vessel wall andexerts a gradually increasing spring force as the tip portion becomescloser to one wall, increasing the force with which the catheter tipportion is held away from the wall as the tip portion comes closer tothe wall, the light spring force permitting some relative movement ofthe catheter tip, and the gradually increasing spring force making itmore difficult for the catheter tip to actually contact the wall.
 15. Amethod of inserting a catheter having a tip retainer assembly attachedat one end thereof into a blood vessel, comprising:placing a sheathinsertion tube assembly within a blood vessel, the sheath insertion tubeassembly including an insertion sheath having handles at a proximal endthereof which are not inserted into the blood vessel, a tip portionwhich is inserted into a blood vessel and a catheter within theinsertion sheath, said catheter having a tip retainer assembly at adistal end of said catheter; maneuvering the insertion sheath assemblywith the catheter therein to a selected position within the bloodvessel; and withdrawing the insertion sheath from the catheter tubewhile maintaining the catheter tube at a fixed position within the bloodvessel, the withdrawal of the insertion sheath causing the tip retainerassembly to be deployed in a spaced position away from the catheter tubesuch that the tip retainer assembly contacts the blood vessel wall witha preselected resilient spring biased force and maintains the cathetertip anchored at a preselected location and held a selected distance fromthe blood vessel wall to prevent the catheter tip from contacting theblood vessel wall.
 16. The method according to claim 15 wherein said tipretainer assembly includes a plurality of wires, the method furtherincluding:selectively extending or retracting said plurality of wires ata distal region of the tip retainer to ensure that the tip retainerassembly contacts the blood vessel wall with sufficient force to retainthe tip spaced from the wall but not with excessive force such as tosignificantly distort the blood vessel wall shape or penetrate throughthe wall.
 17. The method of securing a catheter tip at a selectedlocation in a blood vessel, comprising:inserting a catheter within ablood vessel, the catheter having a tip and a tip retainer assemblyadjacent the tip in a retracted position, the tip retainer assemblyhaving a distal end in a retracted position and including a controlassembly at a proximal end of the catheter outside the blood vessel;maneuvering the catheter tip to a selected location within the bloodvessel; and manipulating the control assembly of the tip retainer todeploy the tip retainer assembly into abutting contact with the bloodvessel wall such that the tip retainer assembly contacts the bloodvessel wall with sufficient force to maintain the catheter tip anchoredat a preselected location and holds the catheter tip in a spacedrelationship from the blood vessel wall to prevent the catheter tip fromrepeatedly contacting the blood vessel wall.